Developing with toner polymer having crystalline and amorphous segments

ABSTRACT

This invention is directed toward a method for obtaining a resinous toner image fixed to a copy substrate. The method involves applying to a copy substrate in image configuration a toner of specific polymeric composition and fixing the image to the copy substrate by the application of heat sufficient to fuse the toner. The toner composition comprises a finely divided mixture comprising a coloring material and a polymeric material which is block or graft copolymer consisting of at least one crystalline or crystallizable polymeric segment chemically linked to at least one amorphous polymeric segment, said crystalline or crystallizable segment individually having a glass transition temperature of less than about 20°C and a melting point of at least about 45°C, and said amorphous segment individually having a glass transition temperature less than the melting point of said crystalline or crystallizable segment. Toner materials according to the present invention exhibit thermal and mechanical properties which render them extremely useful in xerographic processes, particularly high speed process involving contact or flash fusing.

This is a continuation of application Ser. No. 418,628, filed Nov. 23,1973, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to electrophotographic imaging processesinvolving development and fixation of toner images wherein the resinouscomponent of the electrostatographic toner comprises a block or graftcopolymer having crystalline and amorphous segments.

The formation and developement of images on the surface ofphotoconductive materials by electrostatic means is well known. Thebasic electrostatographic process, as taught by C. F. Carlson in U.S.Pat. No. 2,297,691, involves placing a uniform electrostatic charge on aphotoconductive insulating layer, exposing the layer to a light andshadow image to dissipate the charge on the areas of the layer exposedto the light and developing the resulting electrostatic latent image bydepositing on the image a finely divided electroscopic material referredto in the art as "toner". The toner will normally be attracted to thoseareas of the layer which retain a charge, thereby forming a toner imagecorresponding to the electrostatic latent image. This toner image maythen be transferred to a copy substrate such as paper. The transferredimage may subsequently be permanently affixed to the copy substrate suchas by fusion with heat. Instead of forming the latent image by uniformlycharging the photoconductive layer and then exposiing the layer to alight and shadow image, one may form the latent image by directlycharging an insulating layer, which can be either photoconductive ornon-photoconductive, in image configuration. The powder may be fixeddirectly to the insulating layer if desired.

One of the important applications of electrostatography comprises itsuse in automatic copying machines for general office use wherein anelectrostatic latent image is developed using a developer compositioncomprising a carrier mixed with fine particles of resinous toner, andthe thus formed powder image is transferred to a copy substrate and thenfixed thereon. Considerable effort has been expended to provide suitabledevelopers and associated fixing techniques for modern high speedcopying machines. The toner material used must have suitableelectrostatic properties to permit attraction by the carrier and thenselective attraction by the latent images. It must further be physicallystrong to permit constant recycling in a bouncing type of movement. Thetoner must further be resistant to blocking or aggregating at ordinaryoperating temperatures, but yet be capable of being readily fixed to thecopy sheet.

Fixing techniques employing heat, pressure, solvents and variouscombinations thereof have been devised; however, each of these systemsis subject to severe practical limitations which inhere in the systemsthemselves and also the toner compositions heretofore available.Whatever method of fixing is used, speed, effectiveness, and simplicityin operation are the principal, desirable characteristics to beobtained. The most commonly employed fixing techniques employ the use ofheat alone or heat in combination with pressure. The toner materialsemployed must melt or block sufficiently above the ordinary operatingtemperatures of the machines involved to assure convenient storage andhandling. However, the materials must also melt at a practically lowtemperature to avoid excessively-high energy consumption and possibleheat damage to the copy substrate or delicate machine parts.

It has long been recognized that one of the fastest and most positivemethods of applying heat for fusing the powder image to paper is tobring the powder image into direct contact with a hot surface, such as aheated flat plate or roller. However, it was found that as a powderimage is tackified by contact heating, part of the image carried by thecopy sheet would stick to the hot surface so that as the next copy sheetwas contacted with the hot surface, the tackified image partiallyremoved from the first sheet would partially transfer to the next sheetand, at the same time, part of the tackified image from said next sheetwould adhere to the hot surface. This phenomenon is commonly referred toin the printing art as "offset". For a given system, this uppertemperature limit is referred to as the "hot offset temperature". Thus,contact heat fusers are inherently limited to the use of temperaturesand toners which do not cause hot offset of the toner material.

Various types of polymeric materials have been proposed in the prior artfor use as the resinous component in electrostatographic toners. U.S.Pat. No. RE 25,136 teaches toner material based on polystyrene orcopolymers of styrene with monomers such as alkyl methacrylates. BritishPat. No. 1,179,095 teaches toner material based on a combination of twopolymeric materials, one of which polymeric materials has a glasstransition temperature of greater than 20°C, and the other a glasstransition temperature of at least 5°C lower. These polymeric materialsmay be combined by physical admixture, or by forming block or graftcopolymers. Other patents of interest in the electrostatographic tonerarea include U.S. Pat. Nos. 2,788,288; 3,078,342; 3,391,082; 3,502,582;3,510,338; 3,609,082 and 3,647,696. As indicated above, these othertoner materials based on amorphous polymers have not proven entirelysatisfactory when used with contact heat fusers.

While further advances in the art of fixing, including the use of offsetreducing roller surfaces, have provided more suitable means to fusetoner images through the use of heat and pressure with decreased offset,these devices are still restricted to operate within close temperaturetolerances due to the narrow fusing latitudes obtainable with tonermaterials heretofore available. Exemplary of these contact fusingdevices are those disclosed in U.S. Pat. Nos. 3,256,002, 3,268,351,3,291,466, 3,437,032, 3,498,596, and 3,539,161.

SUMMARY OF THE INVENTION

It has now been discovered that electrostatographic toner materialhaving exceptionally desirable mechanical and thermal properties may beprepared by forming a finely divided mixture comprising a coloringmaterial and a polymeric material which is block or graft copolymerconsisting of at least one crystalline or crystallizable polymericsegment chemically linked to at least one amorphous polymeric segment,said crystalline or crystallizable segment individually having a glasstransition temperature of less than about 20°C and a melting point of atleast about 45°C and said amorphous segment individually having a glasstransition temperature less than the melting point of said crystallineor cyrstallizable segment. In the preferred embodiment, the glasstransition temperature of both polymeric segments is less than about 0°C and within the range of about 0° to -100°C, and the melting point ofthe copolymer lies within the range of about 45° to about 150°C. Theamount of amorphous polymer present in the toner copolymers of thisinvention is preferably within the range of about 10 to 90% by weightbased on total polymer weight. Toner materials prepared according to thepresent invention exhibit thermal and mechanical properties which renderthem extremely useful in xerographic processes, particularly high speedprocesses involving heat contact fusing. The thermal properties of theinstant toner materials are such that they exhibit an extremely lowlatent heat of fusion while substantially retaining melting point andmelt crystallization characteristics of toner materials based oncrystalline or crystallizable homopolymers, thereby allowing for a broadlatitude of fusing temperature without toner offset.

DETAILED DESCRIPTION OF THE INVENTION

In pressure roll fixing of electrostatographic toners, threeinterrelated parameters of utmost importance in toner performance are:(1) the minimum fusing temperature, which is the minimum temperaturerequired for fusing the toner; (2) the hot offset temperature, which isthe minimum temperature at which the hot toner melt begins to adhere tothe pressure member, i.e., the maximum temperature of operation whichavoids this type of fixing failure; and (3) the fusing latitude, whichis the operating range defined as the difference between the hot offsettemperature and minimum fusing temperature.

Viscosity-temperature relationships for toner materials have beenestablished, and it is found that a certain viscosity range is requiredfor the onset of fusing. A second, somewhat lower, viscosity range hasbeen found to correspond to offsetting. The difference between theseviscosity ranges is called the "fusing window". The fusing windowdepends to a great extent on specific machine parameters, such ascomponents, configuration, speed, etc. For maximum range of fixingoperation, i.e., maximum fusing latitude, one requires a toner having aminimum temperature dependence on viscosity and maximum traverse of thefusing window.

Whereas toner materials of the prior art containing amorphous polymericmaterial exhibit a minimum fusing temperature usually in excess of150°C, and a fusing latitude in many cases of less than 20°C., it hasbeen found that toner based on crystalline or crystallizable polymersspecifically satisfy the aforementioned thermal and viscosity criteria.Crystalline polymers offer the advantages of relatively sharply definedmelting points above which the polymer can be readily induced to flowand below which at the crystallization temperature (T_(C)) the polymercan be readily induced to harden. Crystalline or crystallizable polymersin general also exhibit less tendency to offset or adhere to fusionrollers even when temperatures of greater than 100°C in the excess ofthe polymer melting point (T_(m)) are encountered during xerographicfusion. In addition, their mechanical properties are such that thesematerials are more resistant to degradation during processing into tonermaterial.

Although the use of toner material based on crystalline orcrystallizable polymers offers some advantages and flexibility in termsof thermal and viscosity criteria particularly in high speed xerographicequipment, one disadvantage lies in the fact that an additional amountof heat energy is required to transform the polymer from a crystallinestate to the state where the polymer will flow and adhere to thetransfer substrate. This heat energy requirement is known as the "Heatof Fusion" and may be defined as the amount of energy necessary intransforming a polymer from a crystalline or a partially crystallinestate to a completely disordered amorphous state without a change intemperature in the crystalline segments of the polymer. The heat offusion is directly relatable to the degree of crystallinity of a givenpolymer: the higher the crystallinity, the greater the heat of fusion,and the greater the amount of heat necessary to melt the polymer.

Thus, whereas crystalline polymers offer certain advantages as indicatedabove, particularly when used as a toner component in a high speedxerographic process, the additional heat necessary for toner fusiontends to mitigate these advantages. In order to overcome the latent heatof fusion and impart the required flowability characteristics into acrystalline polymer such that good adhesion of the toner to thesubstrate will occur, it may be necessary to either heat the tonerbearing recording medium to moderate temperature above T_(M) for aperiod of time longer than might be desirable in a high speed operation,or subject the toner bearing substrate for a desirably short period oftime to a temperature above T_(M) which is in excess of that desirable.In the former case, speed is sacrificed; in the latter case, excessiveheat and the concomitant disadvantages associated therewith may beencountered. In either case, the latent heat of fusion is a factortending to mitigate somewhat the previously recited advantages inureingin toner based on crystalline polymers.

It is thus most advantageous to prepare a toner material which offerssimilar advantages of toner based on a crystalline or crystallizablepolymer in terms of mechanical, physical, chemical and thermalproperties, but which also exhibits a controllably minimal latent heatof fusion. This is accomplished according to the present invention byproviding toner compositions comprising a block or graft copolymercontaining at least one crystalline or crystallizable polymeric segmentchemically linked to at least one amorphous polymeric segment. Tonercompositions based on such segmented copolymers have sharp well definedmelting points with minimal heats of fusion, the heat of fusion of aparticular copolymer being controlled as a function of the ratio ofamorphous to crystalline segments present in the copolymer structure. Ofparticular advantage is the fact that low heats of fusion can beachieved with a minimal effect on the melting point of the copolymer.

The block copolymers can be characterized as materials represented byany of the following generic schemes: [BA]_(n), [AB]_(n), [ABA]_(n), or[BAB]_(n), wherein n is a whole number equal to or greater than 1, Arepresents the amorphous polymeric segment and B represents crystallineor crystallizable polymeric segment. Each segment need not necessarilybe homopolymeric. The individual block segments A and B may be linkeddirectly to one another in head to tail fashion such as by covalentbonding resulting from sequential block copolymerization of theappropriate monomers or by coupling reaction between terminal functionalgroups present on different polymeric molecules. Alternatively, theblock segments may be linked by means of difunctional coupling agentswhich remain in the block copolymer molecules, such as, for example,urethane linkages which would be formed by the reaction of hydroxylterminated polymers with an organic diisocyanate, or ester linkagesformed by the reaction of hydroxy terminated polymers with dicarboxylicacids or carboxy terminated polymers with glycols, or other linkagesformed by reaction of hydroxy terminated polymers with phosgene,dichlorodimethyl silane and the like.

Where the block copolymrs are formed using difunctional coupling agents,the above recited formula schemes for such block copolymers should beconsidered generic to a specific scheme wherein the coupling agentmoiety is present in the block copolymer molecule connecting the Asegment to the B segment. In turn, each A or B segment depictedgenerically above may comprise a plurality of individual A segmentscoupled together or a plurality of B segments coupled together. Thus,for example, the formula [BA]_(n) should, for the purposes of thepresent invention, be considered generic to [B¹ ]-C-[A¹ ] wherein eachB¹ and A¹ segment may consist of a single polymeric molecule or aplurality of polymeric molecules of similar structure coupled together,such as where [B¹ ] is B or [(B-c-(mB] and [A¹ ] is A or [A(-c-A)m],further wherein A and B are as specified above, m is a positive wholeinteger equal to 1 or greater, and c is the coupling agent moiety. Thesame holds true for the three other generic formula schemes recitedabove. Although the coupling technique is preferred because it offersmore precise control over the amounts of each type of polymer introducedinto the polymer chain, it is to be emphasized that any polymerizationtechnique known to those skilled in the art affording the capability ofpreparing the tailor-made block copolymers of the present invention maybe used.

The graft copolymers used as a toner ingredient according to the presentinvention can be categorized generically as branched polymersexemplified by the following schemes:

    (I)  ...AAAAAAAA...  (II)   ...BBBBBBBB...                                         .                      .                                                      B                      A                                                      B                      A                                                      B                      A                                                      .                      .                                                      .                      .                                             

wherein A represents repeating momomeric units contained in theamorphous polymeric segment and B represents repeating monomeric unitscontained in the crystalline or crystallizable polymeric segment. As inthe case of the block copolymers, the A and/or B segments may behomopolymeric or copolymeric. The grafted polymer chain may be presentat any position along the polymer backbone chain, including at the heador tail of the backbone polymer. In most instances a plurality of suchgrafted polymer chains may be present at various points along thebackbone. Where the crystalline or crystallizable polymer comprises thebackbone chain, the degree of branching or grafing is preferably minorin order to preserve the crystalline properties of the graft copolymer;where the grafted side chains comprise the crystalline or crystallizablepolymer, then a larger number of side chains are desirable for the samereason. The graft copolymers may be prepared by techniques well known tothose skilled in the art. Such techniques include creating a freeradical site or sites along a polymer chain by irradiation or othertechnique with subsequent polymerization of monomer in the presence ofthe polymer; introducing active sites along the polymer chain byoxidation to create peroxide groups which act as free radical initiatorswith subsequent polymerization of monomer; and by coupling reactionsperformed by either introducing functional groups along the chain bymetallation or other techniques, or utilizing functional groups alreadypresent, which functional groups can be made to react either directlywith a terminal functional group present in a second polymer orindirectly by means of coupling agents. As is the case with the blockcopolymers, the preferred technique for forming graft copolymersinvolves reacting preformed polymers because of the more precise controlregarding polymer selection and degree of grafting.

Where the block or graft copolymers are prepared by polymerizing amonomer or monomers in the presence of a preformed polymer, the choiceof monomer, catalyst and polymerization conditions must be such that thepolymerizing monomers will form a polymer having the desiredcrystalline, amorphous or isomer structure. Where the preformed polymeris amorphous, the polymerizing monomer and polymerization conditionsshould be such as to lead to the formation of a crystalline orcrystallizable polymer; and vice versa. Sequentially polymerized blockcopolymers are most conveniently prepared by solution polymerizationusing organo-metallic catalysts or the active Ziegler or Natta catalystswhich give rise to the so-called "living polymers;" graft copolymers aremost conveniently prepared by solution or suspension polymerizationinvolving dissolving or dispersing the backbone polymer in a liquidmedium which medium contains grafting monomer, free radical initiatorand polymerization catalyst.

The number average molecular weight of the copolymers employed in thetoner compositions of the present invention should be within the rangeof about 5,000 to 200,000 g/mole for best results. At molecular weightsof less than about 5,000 it is found that the copolymer may exhibit hotoffsetting due to the low melt viscosity encountered at this lowmolecular weight; above about 200,000 g/mole, the copolymer is moredifficult to fuse or fix in the xerographic process. The preferred rangefor optimum hot melt properties is about 15,000 to 150,000 g/mole. Theindividual amorphous or crystalline polymer segments forming the blockor graft copolymer preferably have a number average molecular weightwithin the range of about 1,000 to 20,000 g/mole, with a preferred rangeof about 2,000 to 12,000 g/mole.

As indicated above, segmented copolymers derived from monomerspolymerized to form crystalline or crystallizable polymers having acrystalline T_(M) in the range of about 45° to 150°C and a T_(G) withinthe range of about 20° to -100°C are particularly suitable for thepurposes of this invention. Examples of suitable genus and speciespolymers are: Polyesters, including polyalkylene polyesters wherein thealkylene group contains at least two carbon atoms such aspolydecamethylene sebacate, polydecamethylene succinate, polyethylenesebacate, polyethylene succinate, polyhexamethylene sebacate,polyhexamethylene suberate, polyhexamethylene succinate and the like;aromatic polyesters such as poly-p-xylene adipate or polydiethyleneglycol terphthalate; polyvinyl esters and ethers such as polyvinyl ethylether, polyvinyl butyl ether, polyvinyl 2-methoxyethyl ether, polyvinylstearate and the like; polysulfides and sulfones such aspolydecamethylene sulfide, polyhexamethylene sulfide, polytetramethylenesulfone and the like; polyethers such as polybutadiene oxide,polyethylene oxide, polypropylene oxide and the like; polyepihalohydrinssuch as polyepifluorohydrin; polyenes including cis and trans polydienessuch as cis 1, 4 polybutadiene and 1,2 trans polybutadiene; polyolefinssuch as poly-1-pentene, poly-1-hexadecene, polybutene,poly-3-methyl-1-butene and the like; cellulose polymers such ascellulose tricaprate; polyacrylates such as polyisobutyl acrylate;polyacids; polyamides; polyurethanes; and like polymers. Copolymersderived from monomers constituting two or more of the above polymers mayalso be used. Particularly preferred as crystalline segments in theblock or graft copolymers are those polymers and copolymers having aT_(M) within the range of about 55°C to about 120°C.

The amorphous segment of the block or graft copolymers may similarly beselected from a wide variety of polymeric materials having a T_(G) lessthan the T_(M) of the crystalline polymer segment with which it is to beassociated in the block or graft copolymer. The T_(G) of the amorphoussegment is preferably less the 0°C. Examples of suitable amorphouspolymers include atactic polymers derived from the same or differentmonomers or monomer isomers used to form the crystalline orcrystallizable segment of the copolymer recited above, said monomerspolymerized under conditions such that atactic rather than isotacticstructure results. Suitable classes of amorphous polymers includepolyvinyl ethers; atactic polyolefins; polyacrylates; polyoxides such aspolypropylene oxide; polysulfides; unsymmetrically branched polyestersand polyamides; aliphatic polyurethanes; and like materials.

It has been further found that electrostatographic or triboelectricproperties of the present toner materials may be optimized and bestcontrolled by employing isomeric copolymers, that is, copolymers whereinthe crystalline and amorphous segments have identical chemicalcompositions but, of course, different chemical structures. Examples ofsuch copolymers would be block or graft copolymers wherein thecrystalline segment comprises polybutene-1 or -2, and the amorphoussegment comprises polyisobutylene; copolymers wherein the crystallinesegment is polyhexamethylene sebacate and the amorphous segment ispoly-(2-methyl, 2-ethyl, 1,3-propylene sebacate). Other combinationsinclude isotactic poly (vinyl n-propyl ether) and atactic poly (vinylisopropyl ether; poly (trimethylene sulfide) and poly (propylenesulfide); poly (hexamethylene oxide) and atactic poly (vinyl butylether); isotactic poly (isobutyl acrylate) and atactic poly (n-butylacrylate). Other isomeric combinations will occur to those skilled inthe art.

As indicated above, for best results the segmented copolymers shouldexhibit a T_(m) within the range of about 45°C to about 150°C and aT_(G) within the range of about 20°C to -100°C. In order to avoid thepossibility of blocking under extreme conditions, it may be desirable toselect crystalline and amorphous segments such that the copolymers havea T_(m) in excess of about 55°C and a T_(G) of less than 0°C.

The block or graft copolymers may be fabricated into electrostatographictoner using any of the known techniques of the prior art by mixing thecopolymers with a colorant material. Mixing may be accomplished bydispersing the colorant in the melted copolymer, hardening the polymerand pulverizing the composition in a device such as a jet or hammermillto form it into small particles. Alternatively, mixing may be carriedout by combining the colorant with a solution, dispersion or latex ofthe copolymer, followed by recovery of the copolymer/colorant mixture infinely divided form by spray drying techniques. Suitable methods ofmixing are more thoroughly described in U.S. Pat. No. 3,502,582. Theaverage particle size of the processed toner should be within the rangeof about 1 to 30 microns, preferably between about 3 to 15 microns. Asubsequent screening or sizing operation may be necessary to produce atoner having this particle size distribution.

The colorant material used in preparing the toner composition mayinclude any pigment or water or organic solvent soluble dye. The mostcommon pigments used in electrostatographic toner materials are finelydivided carbon black, cyan, magenta and yellow pigments. The most commondyes are the acid, basic and dispersed dyes of suitable color as areknown in the art. Typical examples of suitable colorants are discussedin U.S. Pat. No. 3,502,582. The pigment or dye should be present in theamount effective to render the toner highly colored so that it will forma clearly visible image on a recording member. Preferably, forsufficient color density the pigment is employed in an amount from about1% to about 20% by weight, based on the total weight of the color toner.If the toner colorant employed is a dye, quantities substantiallysmaller than about 1% by weight may be used.

The toner composition may be formulated into an electrostatographicdeveloper composition by combining the finely divided toner with asuitable carrier material such that the toner forms a coating on thecarrier. The toner and carrier material may be premixed or mixed insidethe developer region of the xerographic machine. Where the developmentprocess in the well known magnetic brush process, the carrier materialwill be a magnetically attractive material such as finely divided ironparticles of about 60 to 120 mesh size. For other than magnetic brushdevelopment, the carrier material may be of any of the known particulatesubstances exhibiting appropriate triboelectric effects such that thecarrier particles impart a charge to the finer toner whereby the toneradheres to and coats each carrier particle. Examples of suitablecarriers are inorganic salts, glass, silicon and other materials such asdisclosed in the aforementioned U.S. Pat. No. 3,502,582. The particlesize of the carrier should be significantly greater than the toner,preferably within the range of about 50 to 1000 microns. The toner ismost effectively employed at a level from about 0.5 to 10 parts byweight per 100 parts by weight of carrier material.

The toner and developer compositions of the present invention may alsocontain any of the additives known to be included in such compositionssuch as lubrication aids, antioxidants, sensitizing agents, polymeric ornon-polymeric plasticizers, and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following specific embodiment illustrates the preparation of tonermaterial wherein the polymeric component comprises an isomeric blockcopolyester prepared by coupling crystalline poly (hexamethylenesebacate) [poly HMS] and amorphous poly (2-methyl-2-ethyl-1,3-propylenesebacate) [poly MEPS] using hexamethylene diisocyanate as the couplingagent whereby urethane linkages are formed. The block copolyester wasprepared by initially individually synthesizing polyHMS and poly MEPS,and then subjecting a mixture of these homopolymers to a couplingreaction as hereinafter described.

EXAMPLE 1

Crystalline poly (hexamethylene sebacate) was prepared using a kettleequipped with a stirrer, nitrogen gas inlet tube, thermometer andcondenser by reacting sebacic acid with 1,6hexamethylene glycol in thepresence of a p-toluenesulfonic acid catalyst as follows: sebacic acidand hexamethylene glycol were added to the reaction kettle in arespective 1.0 to 1.1 molar ratio along with 0.5 wt % p-toluenesulfonicacid. The 10 mole % excess of glycol was used to ensure the predominantpresence of hydroxyl end groups in the reaction product. The mixture washeated to 165°C while stirring. At 165°C, an amount of xylene was addedto assist refluxing and this temperature was maintained until waterevolution ceased (4 hrs.). Afterwards, the condensers were removed andthe excess glycol and catalyst were removed by sparging with nitrogenfor 0.5 hours at 165°C. On cooling to room temperature, the poly(hexamethylene sebacate) crystallized into an off-white solid. Next, thepoly (HMS) from above was purified by precipitation from a benzenesolution into methanol using techniques well known in the art. Theprecipitated poly (HMS) was collected by filtration and dried in vacuo.Analytical data on this purified material indicate an acid number of1.06, an hydroxyl number of 34.4, an M_(n) of 3165 g/mole, an MWD (M_(w)/M_(n)) of 1.41 by GPC in chloroform, a glass transition temperature ofabout -62°C and a crystalline melting point of about 65°C.

EXAMPLE 2

Amorphous poly (2-methyl-2 -ethyl-1,3-propylene sebacate) was preparedby reacting sebacic acid and a 10 mole % excess of2-methyl-2-ethyl-1,3-propylene glycol in the presence of 0.5 weight %p-toluenesulfonic acid in the same manner as in Example 1. On cooling toroom temperature after the polymerization, the poly (MEPS) remained as aclear, tacky fluid. Analysis indicates it has an acid number of 2.40, anhydroxyl number of 19.4, an M_(n) of 5150 g/mole, an MWD of 1.87 by GPCin chloroform, and a glass transition temperature of about -61°C.

EXAMPLE 3

A block copolyester was prepared by coupling the hydroxy terminated poly(HMS) prepared in Example 1 and the hydroxy terminated poly (MEPS)prepared in Example 2 using hexamethylene diisocyanate as the couplingagent according to the following procedure: three parts by weight ofpoly (HMS) of Example 1 were mixed with one part by weight of poly(MEPS) of Example 2 in a reaction kettle equipped with a stirrer,nitrogen gas inlet tube, thermometer and condenser. The mixture washeated to 135°C with stirring, and hexamethylene diisocyanate was addedat a level of 4.5% by weight of the fluid polymeric mixture. Thetemperature was maintained at 135°C. Within 10 minutes the viscosity wassuch that the polymeric mass began to envelop and climb the stirrer. Thecoupling reaction was terminated after 1 hour and the copolymer wasdissolved in benzene and precipitated with stirring into methanol. Theprecipitate was collected by filtration, washed thoroughly with methanoland dried in vacuo. A yield of about 89% was realized from this couplingreaction. The block copolyester was analyzed by Nuclear MagneticResonance to contain 78.6% poly (HMS) and 21.4% poly (MEPS). It had anintrinsic viscosity in chloroform of 0.90 dl/g at 25°C, a molecularweight believed to be about 45,000 ± 15,000 g/mole, crystalline meltingpoint of about 63°C, and a glass transition temperature of about -60°C.

Although the structure of the block copolymer molecules producedaccording to Example 3 is not precisely known, it is believed thatbecause of the predominant presence of segments of polymerized (HMS) inthe block copolymer, the copolymer statistically comprises a pluralityof repeating crystalline poly HMS segments connected by urethanelinkages, said repeating segments in turn connected by urethane linkageswith the amorphous poly (MEPS) segments at various random points alongthe block copolymer chain, such as illustrated in the following scheme:

    . . . B-c-B-c-B-c-A-c-B . . .

wherein

B represents polymerized (HMS)

A represents polymerized (MEPS)

and C represent ##EQU1## This segment of structure conforms to thegeneric structure BAB, a species of which generic structurre for thiscopolymer is

    [B.sup.1 ]-c-[A.sup.1 ]-c-[B.sup.11 ],

wherein

B¹ is [-(B-c-)₂ B]

A¹ is A

and B¹¹ is B

EXAMPLE 4

A xerographic toner material was prepared by forming a mixture of theblock copolyester of Example 3 and a finely divided pigment grade carbonblack.

A mixture comprising 95 parts by weight of the block copolyester ofExample 3, and 5 parts by weight of Molocco H carbon black was formed byheating the copolyester to a temperature above its melting point,dispersing therein the carbon black, and mixing until a uniformdispersion of the carbon black in the block copolyester was obtained.The mixture was then quick cooled to a temperature below the meltingpoint of the block copolyester.

Finely divided toner material having an average particle size in theorder of about 20 microns was prepared by comminuting the above mixturefirst in a Fitz mill and subsequently in a jet pulverizer.

The toner was tested by employing it as the toner in a "Xerox 3600" copymachine embodying a contact heat fusing device and found to produce verysatisfactory copies without toner offset on the fusing roll.

EXAMPLES 5 - 11

Several additional samples of isomeric block copolyesters having variousratios of poly (HMS) and poly (MEPS) were prepared by coupling the poly(HMS) of Example 1 and the poly (MEPS) of Example 2 using variouscoupling agents. Synthesis data for these copolyesters is shown in Table1.

The block copolyesters of Examples 5, 7, 9, 10 and 11

                                      TABLE I                                     __________________________________________________________________________           Poly HMS   Poly MEPS                   % HMS in                        Sample (parts by weight)                                                                        (parts by weight)                                                                        Coupling Agent                                                                          Yield (%)                                                                            Copolymer                                                                            T(m)                     __________________________________________________________________________                                                         Copolymer                Ex  5  15.0       15.0       (CH.sub.2).sub.6 (NCO).sub.2                                                            91.4   56.3   60°C              Ex  6  3.8        6.2        COCl.sub.2                                                                              70.0   56.8   60°C              Ex  7  3.8        6.2        (CH.sub.2).sub.6 (NCO).sub.2                                                            83.0   50.3   58°C              Ex  8  3.8        6.2        (CH.sub.3).sub.2 Si CL.sub.2                                                            61.0   47.2   57°C              Ex  9  6.22       10.3       (CH.sub.2).sub.6 (NCO).sub.2                                                            87.0   40.6   55°C              Ex 10  6.33       10.3       C.sub.6 H.sub.4 (NCO).sub.2                                                             90.4   38.8   55°C              Ex 11  7.5        22.5       (CH.sub.2).sub.6 (NCO).sub.2                                                            84.4   28.0   53°C              __________________________________________________________________________

were prepared by the method of Example 3; with regard to the blockcopolyesters of Examples 6 and 8, the procedure of Example 3 wasmodified somewhat in that refluxing was carried out in chlorobenzene(132°C) containing a small amount of pyridine. General techniques forpreparing linear copolyesters using coupling agents are known in the artas, for example, disclosed in U.S. Pat. No. 2,691,006.

The copolymers of Examples 5 - 11 were each processed into tonermaterial by the method of Example 4 and each performed satisfactorilywhen used in a xerographic machine.

As indicated above, toner materials based on the segmented copolymers ofthe present invention exhibit minimal latent heats of fusion and at thesame time the sharp, well defined melting points desirable in a tonermaterial. This may be illustrated by a comparison of the latent heats offusion (ΔH_(u) -- in calories/gm.) and melting points (T_(m)) for aplurality of polymer samples containing polymerized hexamethylenesebacate (HMS) and polymerized 2 methyl-2-ethyl-1,3-propylene sebacate(MEPS).

EXAMPLE 12

A series of homopolymer blends having various weight ratios betweenabout 20-80% of poly (HMS) and poly (MEPS) were prepared by formingintimate admixtures of the poly (HMS) prepared according to Example 1and the poly (MEPS) prepared according to Example 2.

A series of block copolymer samples having various weight ratios betweenabout 20-80% of poly (HMS) and poly (MEPS) were prepared according tothe process of Example 3.

A series of random copolymers also having various weight ratios betweenabout 20-80% of polymerized HMS and polymerized MEPS were prepared by aprocess similar to that described in Example 1 by reactingsimultaneously a mixture of 1, 6 hexamethylene glycol,2-methyl-2-ethyl-1,3 propylene glycol and sebacic acid. Variouscopolymer compositions were achieved by alterning, systematically, themolar ratio of the two diols in the condensation reacton with sebacicacid. The copolymers so prepared exhibit M_(n) values within the rangeof about 2200 to 3600 g/mole.

Samples of each type of polymer composition for various levels ofpolymerized HMS content were evaluated for latent heat of fusion andcrystalline melting point data, the results plotted, and the plotsinterpolated at 80%, 60%, 40%, and 20% HMS content. Results are shown inTable 2.

                  TABLE 2                                                         ______________________________________                                        %        Random      Homopolymer Block                                        HMS      Copolymer   Blend       Copolymer                                           T.sub.m                                                                             ΔH.sub.u                                                                        T.sub.m ΔH.sub.u                                                                      T.sub.m                                                                             ΔH.sub.u                       ______________________________________                                        100%     65°C                                                                           30      65°C                                                                         30    65°C                                                                         30                                 80%      57°C                                                                           <10     64°C                                                                         25    63°C                                                                         17                                 60%      42°C                                                                           --      62°C                                                                         18    61°C                                                                         11                                 40%      22°C                                                                           --      62°C                                                                         12    56°C                                                                          7                                 20%       0°C                                                                           --      61°C                                                                          6    55°C                                                                          6                                 ______________________________________                                    

As can be seen from Table 2, the melting point of the random copolymersdrops off rapidly as the % HMS in the random copolymer is decreased witha corresponding increase in % MEPS. Below about 60% HMS, the copolymersare a viscous fluid unsuitable for use in a toner composition. With thehomopolymer blends, the lowering of T_(m) is much less severe, butΔH_(u) is found to drop off in almost direct proportion to the amount ofpoly (HMS) in the blend. With the block copolymers, the lowering ofT_(m) is somewhat greater than in the blend, but still quite acceptablefor toner use, but most significantly the drop in ΔH_(u) is much higherthan in comparable samples of the blend. Thus considerably less heatenergy is required to melt or fuse toner based on the block copolymersthan is required to melt toner based on the homopolymer blend.

Although the toner composition of the present invention may be used inelectrophotographic processes embodying any of the well known techniquesof image fixation or fusing such as radiation, vapor, or liquid fusing,it is employed most advantageously in processes involving contactfusing, as discussed above, or flash fusing such as for exampledisclosed in U.S. Pat. Nos. 3,465,203, 3,474,223, and 3,529,129. In eachof these processes, exposure of the image recording medium bearing thepowdered toner image, usually paper, to a source of heat is for anextremely limited time duration. In contact fusing, a moving recordingmedium is exposed to heat while the medium passes through a nip formedby a heated pressure roller and a second support roller. With radiantflash fusing, the recording medium is exposed to heat energy in the formof electromagnetic waves generated usually by a gas lamp, such as axenon lamp, for a period of timed measured in milliseconds. With each ofthese processes, a maximum amount of heat energy sufficient to properlyfuse the toner without scortching the recording medium is required overa short period of time. It is thus evident that the toner compositionsof the present invention having sharp well defined melting points andcontrollably minimal latent heats of fusion respond particularly wellfor use in processes involving such fusing techniques.

While the invention has been described with reference to the embodimentsdisclosed herein, it is not confined to the specific embodiment setforth, and this application is intended to cover such operativemodifications or changes as may come within the scope of the followingclaims.

What I claim is:
 1. In an electrophotographic imaging process includingthe steps wherein a particulate electrostatographic toner composition isapplied in image configuration to the surface of a recording member, andsaid recording member bearing said toner composition in imageconfiguration is subjected to heat or heat and pressure sufficient tofuse said toner composition to the surface of said recording member, theimprovement which comprises conducting said imaging process using afinely divided toner composition comprising a uniform mixture of:a. acolorant material and b. a polymeric material, said polymeric materialcomprising a segmented copolymer consisting of at least one crystallineor crystallizable polymeric segment chemically linked to at least oneisomeric amorphous polymeric segment, said segmented copolymer having aglass transition temperature of less than about 20°C and a melting pointof at least about 45°C.
 2. The process of claim 1 wherein said polymericmaterial has an average molecular weight within the range of about 5,000to 200,000 grams per mole and a melting point within the range of about45°C to about 150°C.
 3. The process of claim 2 wherein said polymericmaterial is a block copolymer having a formula selected from the groupconsisting of: [BA]_(n), [AB]_(n), [BAB]_(n), and [ABA]_(n), wherein Arepresents the amorphous polymeric segment, B represents the crystallineor crystallizable polymeric segment, and n is a whole number equal to 1or greater.
 4. The process of claim 3 wherein the average molecularweight of said A or B polymeric segments is within the range of about1,000 to 20,000 grams per mole.
 5. The process of claim 2 wherein saidsegmented copolymer is prepared by chemically reacting at least twopreformed polymers, one of said preformed polymers being crystalline orcrystallizable and having a glass transition temperature within therange of about 20°C. to -100°C. and a melting point within the range ofabout 45°C. to 150°C., and another of said preformed polymers beingamorphous and having a glass transition temperature of less than 45°C.6. An electrophotographic imaging process comprising the steps ofsubjecting the surface of a charged photoconductive insulating layer toa pattern of light and shadow such that an electrostatic latent image isformed on the surface of said layer, developing said latent image bycontact of said surface with a developer composition comprising amixture of carrier particles and toner material, transferring the tonermaterial in image configuration from said surface to the surface of arecording member, and heating the surface of said recording membersufficient to fuse said toner composition to the surface of saidrecording member, said toner material comprising a finely dividedcomposition comprising a uniform mixture of:a. a colorant material andb. a polymeric material, said polymeric material comprising a segmentedcopolymer consisting of at least one crystalline or crystallizablepolymeric segment chemically linked to at least one isomeric amorphouspolymeric segment, said segmented copolymer having a glass transitiontemperature of less thant about 20°C, a melting point of at least about45°C., and an average molecular weight within the range of about 5,000to 200,000 grams per mole.
 7. The process of claim 6 wherein saidpolymeric material is a block copolymer having a formula selected fromthe group consisting of: [BA]_(n), [AB]_(n), [BAB]_(n), and [ABA]_(n),wherein A represents the amorphous polymeric segment, B represents thecrystalline or crystallizable polymeric segment, n is a whole numberequal to 1 or greater, and wherein the average molecular weight of eachA or B polymeric segments is within the range of about 1,000 to 20,000grams per mole.
 8. The process of claim 6 wherein said segmentedcopolymer is prepared by chemically reacting at least two preformedpolymers, one of said preformed polymers being crystalline orcrystallizable and having a glass transition temperature within therange of about 20°C. to -100°C. and a melting point within the range ofabout 45°C. to 150°C., and another of said preformed polymers beingamorphous and having a glass transition temperature of less than 45°C.9. The process of claim 8 wherein said segmented copolymer is a blockcopolyester having one or more repeating units of crystalline polyesterchemically linked to one or more repeating units of amorphous polyester.10. The process of claim 6 wherein said colorant material is present ata level of from about 1% to about 20% by weight of said composition. 11.The process of claim 10 wherein the average particle size of the tonerparticles is within the range of about 1 to 30 microns.
 12. The processof claim 11 wherein the developer composition comprises from about 0.5to 10% by weight of toner particles and about 90 to about 99.5% byweight of carrier particles, said carrier particles having an averageparticle size greater than the toner particles whereby the tonerparticles adhere to and coat each carrier particle.
 13. The process ofclaim 6 wherein said heating is carried out by passing the recordingmember through a zone of heat and pressure.
 14. The process of claim 6wherein said heating is carried out by exposing the developed surface ofthe recording member to electromagnetic radiation.